The assignee of the present invention manufactures and deploys spacecraft for, commercial, defense and scientific missions. Many such spacecraft operate in a geosynchronous orbit having a period equal to one sidereal day (approximately 23.93 hours).
A particular type of geosynchronous orbit is a geostationary orbit (GSO), characterized as being substantially circular and co-planar with the Earth's equator. The nominal altitude (the “GEO altitude) of a GSO is approximately 35,786 km. An elevation angle from a user located on the Earth to a satellite in GSO is a function of the user's latitude. When a service area on the ground intended to receive communications or broadcast services (hereinafter, an “intended service area”) is at a north or south latitude above approximately 60 to 70 degrees, the elevation angle is small enough that service quality is significantly impaired.
To mitigate this problem, satellites operable in highly inclined, highly elliptical geosynchronous orbits have been proposed, as described, for example in Bigras, et al., US Pat. Pub. 2014/0017992 (hereinafter, Bigras) the disclosure of which is hereby incorporated in its entirety into the present patent application. A geosynchronous, highly inclined, elliptical orbit (HIEO) may be selected such that the orbit's apogee is located at a pre-selected, substantially constant, longitude and latitude. A satellite operating in an HIEO can, during much of its orbital period (e.g., sixteen hours out of twenty four) enable higher elevation angles to a user than a GSO satellite. Two such satellites co-located in substantially identical orbits, but separated in phase by 180 degrees can provide continuous coverage to an intended circumpolar intended service area above 60 degrees latitude. The altitude of apogee of the HIEO disclosed by Bigras is approximately 48,000 km, whereas the altitude of perigee is approximately 23,000 km. Where the intended service area is in the northern hemisphere, the argument of perigee (the angle in the orbital plane measured, in the direction of satellite motion, from the orbit's ascending node to the orbit perigee) for such an orbit is desirably about 270 degrees. With an argument of perigee of 270 degrees, the orbit apogee is located above the northern hemisphere and the orbit perigee is located above the southern hemisphere. Where the intended service area is in the southern hemisphere, the argument of perigee is desirably about 90 degrees. With an argument of perigee of 90 degrees, the orbit apogee is located above the southern hemisphere and the orbit perigee is located above the northern hemisphere.
In the absence of the presently disclosed techniques, a launch vehicle with a restartable upper stage may inject the satellite directly into the geosynchronous HIEO. The mass that a Proton launch vehicle can deliver from the Baikonur launch complex to the geosynchronous HIEO is about 3500 kg, which is roughly equivalent to the beginning of life mass of a single satellite with typical lifetime and payload characteristics. Thus, using conventional techniques, two launches, each launch being dedicated to a single satellite, would be required to provide continuous coverage to the intended circumpolar service area.
Considering the high cost of a launch vehicle, improved techniques increasing an effective payload capacity of the launch vehicle are desirable.